1. Field of the Invention
This invention relates to accessories for paper used in electro-mechanical printers connected to computers used in data processing and related applications. More particularly, the invention relates to an accessory which minimizes tearing of perforated continuous sheets of paper, of the type having circular perforations on opposite sides of the paper for engagement by the sprocket pins of a printer tractor-feed mechanism.
2. Description of Background Art
Electro-mechanical printers are used extensively as output devices for computers, providing a permanent printed record on paper, referred to as "hard copy" of data stored in the computer. The hard copy description is used to differentiate printed data from data displayed temporarily on the cathode ray tube (CRT) screen or other visual data output display device used with the computer. Computer driven printers are also used extensively to print letters, forms and envelopes in applications referred to collectively as word processing.
One or the other of two different types of mechanisms are commonly used to feed paper through computer printer mechanisms. One type of paper feed mechanism uses a pair of elongated cylindrical rollers having resilient surfaces which exert pressure on opposite sides of a sheet of paper, and are rotated in opposite directions to draw the paper longitudinally between the rollers. This type of feed mechanism, which is sometimes referred to as a friction drive, is used in most typewriters.
A second type of paper feed mechanism commonly used in computer printers uses a pair of parallel, laterally spaced apart, coaxial "tractor" wheels to feed paper through the printer. In this type of feed mechanism, frequently referred to as a tractor mechanism or tractor-feed mechanism, the tractor-feed wheels have radially outwardly projecting pins or sprockets, spaced at regular intervals along the outer circumference of each wheel. The spacing between tractor pins is chosen to match the longitudinally spacing between circular perforations provided on opposite lateral sides of perforated computer paper, which is usually supplied as long, continuous sheet. Customarily, perforated computer paper is supplied as a zig-zag (fan-folded) sheet which can fit in a box of compact size.
Tractor feed printers have certain advantages over friction roller printers. Thus, the lateral positioning of characters printed on paper fed by a tractor-feed mechanism is precisely repeatable, while paper fed by a friction roller mechanism can move laterally with respect to the printing elements. Also, paper fed by friction rollers may become skewed diagonally with respect to the feed direction, causing the printed lines to be inclined from the horizontal. In tractor feed printers, the fixed geometrical relationship between tractor wheel sprockets and paper perforations prevents line skew from occurring.
A disadvantage of tractor-feed mechanisms is their tendency to sometimes tear paper fed through the mechanism. This is particularly likely to occur at the time the leading edge of a strip of perforated paper is first fed into the mechanism, when only a single pair of laterally paired holes at the leading edge of the strip are engaged by tractor wheel pins. At this point, longitudinal stress on the paper is greatest, as is the likelihood that the paper will tear. This susceptibility to tearing is particularly great for paper sheets which are scored along lateral and longitudinal edges, to permit tearing off single sheets of paper after they have been fed through the printer. Scored or partially perforated paper of this type is used to print computerized letters on letterheads which appear to have been individually typed, a ploy commonly used by politicians in sending mass mailings to their constituents.
Obviously, it would be desirable to minimize the loss of perforated computer paper due to tearing by a printer tractor mechanism. This is especially true of perforated computer paper which bears scored, pre-printed forms such as letterheads, since these are substantially more expensive than blank or stock computer paper. Moreover, the time which must be taken by the printer operator to remove torn paper and re-insert a fresh, untorn edge present a significant economic waste. With these considerations in mind, the present invention was conceived.
In searching the literature for articles possibly related to the subject matter of the present invention, the following peripherally related patents were found:
Weingarten, U.S. Pat. No. 4,448,558, May 15, 1984, Computer Printer Paper Support
Discloses an accessory for supporting unperforated papers, forms, stationery and the like for advancement through the pin feed mechanism of a computer printer or the like. The accessory comprises a pair of flexible strips each having near one longitudinal edge thereof a plurality of regularly spaced holes for engaging the sprockets of the pin type feed mechanism of a computer printer or the like. Near the other longitudinal edge of each strip is a strip of non-setting, non-permanent adhesive for firmly, but removably securing papers for advancement into the printer.
Swiss Patent 61,442, Lauener, July 5, 1912, Card Holder Typewriters
Discloses a card or sheet approximately the size of a sheet of typing paper having tabs a and b for supporting post cards and the like for advancement into the typewriter.
German Patent 1,149,726, June 6, 1963, Jung, Conveyor Band
Discloses a conveyor band for moving in overlapping fashion envelopes, bags, cards, etc., through a tabulating machine, typewriter, etc. The band has marginal perforations and is folded so as to form pockets. The depth of the pockets is determined by the size of the envelopes, etc., and by the perforations.
French Patent, 2,595,625, Sept. 1987, Gran, Support For Papers Fed Through Printer
Discloses supports for papers fed through a tractor printer comprising a pair of perforated strips having self-adhesive tabs for non-setting attachment to the papers to be fed through the printer.
None of the above-cited patents, nor any other prior art which the present inventor is aware of, discloses a solution to the specific tearing problem described above.